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ANk KLEINFELDER 6. Page 4, paragraph 2 - permeability citation appears in error-suggest deleting or correcting second sentence. The permeability values given on page 4 are intrinsic permeability which has units of cm2 as opposed to hydraulic conductivity which has units of cm/sec or m/day. Environmental Health Division Comments and Response 1. Leachate control during closure is required. More specific information will be necessary regarding how the monitoring system will work. Installation of the final cap will reduce rainwater infiltration to insignificant levels. Consequently, leachate generation will reduce accordingly since infiltrating rainwater is the primary source of water for leachate generation. Therefore, the final cap will provide leachate control during closure. The landfill is unlined and does not have a leachate collection system. Hence, there is no way to collect (and monitor) leachate production during postclosure. For these reasons, leachate monitoring was not proposed in the Closure Plan. 2. More specific information about the membrane liner proposed for the barrier layer of the final cap is required. Depending on market conditions, one of two barrier layers (geomembrane) will be used, either polyvinyl chloride (PVC) or high density polyethylene (HDPE). As explained in the Closure Plan, Section 11.1.2.2.1, either material is suitable for use as a barrier layer in a landfill cap. If PVC is selected, the thickness of the geomembrane will likely be 40 mil. If HDPE is selected, the thickness of the geomembrane would be either 40 or 60 mil. 60 mil is commonly used for durability during construction and easier seaming. Both materials would be heat seamed, most likely with a dual hot wedge device which allows quick and reliable leak testing of hundreds of feet of seam in one step. HDPE is delivered to the landfill site in rolls. For 60 mil HDPE, a typical roll is 22.5 feet wide and 1.5 to 2 feet in diameter weighting approximately 2,800 to 3,000 pounds. The roll contains 420 feet of geomembrane. A piece of heavy equipment, typically a front end loader, supports the roll with a device called a spreader bar and then unrolls the sheet onto the prepared foundation layer. The sheet is then seamed to the adjacent sheet and the seams leak tested. This process is repeated until the entire barrier layer is completed. After the barrier layer is complete, the vegetative layer(soil) is then placed on top of the barrier layer. PVC is more flexible than HDPE and can be handled differently. Companies known as fabricators take rolls of PVC geomembrane from the geomembrane manufacturer and then factory seam the individual lengths of PVC to form panels that can be up to 1 acre in size. These panels are sized according to the needs of individual projects. The large panels are then folded into a cube known as a crate. A crate formed by folding approximately 16,000 square feet of 40 mil PVC would be approximately 46"x88"x48" high and weights approximately 4,000 pounds. The crates are delivered on site and then placed so that once the geomembrane in unfolded, it will be properly positioned for seaming. As with HDPE, the vegetative layer is then placed on top of the barrier layer. 3. Methane gas monitoring is required. Submit gas monitoring plan and explain how the monitoring system will be modified for changing postclosure use. 23-481399-A00/TL960001 Page 4 of 5 January 4, 1996 Copyright 1996 Kleinfelder,Inc.